[1][2] While in high school, Allen played varsity football only in his senior year and also ran on the track and field team.

[2] Allen posted 120 tackles and 5 interceptions in his career with the Bulldogs football team of The Citadel, The Military College of South Carolina, returning two for touchdowns.

[2] Following Citadel's victory over Samford on October 31, the Southern Conference named Allen the Defensive Player of the Week for six solo tackles and two interceptions returned for 110 yards.

[2] Allen would again earn second-team honors in his senior season (2010), having made 23 tackles (13 solo), 6 passes defended (most in the team), and 2 interceptions (returned for 18 yards).

At the Citadel's Pro Day on March 28, 2011, he stood on his combine numbers but performed the vertical again, posting 37 1/2 inches this time.

Scouts were very high on his physical tools and size but said he had to develop his awareness and was a raw prospect lacking the natural coverage instincts that are needed to be an NFL starter.

[5] In Week 2 (September 18), Allen and Arnaz Battle made a special teams tackle of the Seattle Seahawks' Leon Washington during a third quarter kickoff return.

Defensive coordinator Dick LeBeau commented about Allen: "We always liked his size to speed ratio and he's got an innate feel for the ball.

[14] Allen made a career-high five tackles in Week 6 (October 11), a Thursday night match against the Tennessee Titans.

[5] In Week 16 (December 23) against the Cincinnati Bengals, Allen picked off two passes from Andy Dalton and returned the interceptions for a cumulative 6 yards.

[15] In the season finale on Week 17 (December 30) against the Cleveland Browns, Allen forced two fumbles, both of which were followed by Steelers touchdowns.

Allen struggled with injuries during the 2013 season, as well as the return of veteran cornerback William Gay to the Steelers after a 1-year stint with the Arizona Cardinals.